1. Field of the Invention The present invention relates generally to a fluid-filled type vibration damping device capable of generating vibration damping effect utilizing a non-compressible fluid sealed therein. More particularly, the present invention pertains to a fluid-filled type vibration damping device which is furnished with a resin bracket.
2. Description of the Related Art
Fluid-filled type vibration damping devices are known as one type of damping connectors or damping supports adapted to be mounted between components that make up a vibration transmission system. Such devices utilize flow behavior or the like of a non-compressible fluid sealed therein so as to obtain vibration damping effect, in addition to vibration damping effect owing to a rubber elastic body. One example of these vibration damping devices comprises a first mounting member and a tubular second mounting member connected by a main rubber elastic body, a fluid chamber whose wall is partially defined by the main rubber elastic body and surrounded by the tubular second mounting member, and a non-compressible fluid sealed within the fluid chamber.
Such a fluid-filled type vibration damping device is installed by the first mounting member and the second mounting member being attached respectively to components to be provided with vibration damped linkage. For example, in a vehicle-use engine mount that serves as a fluid-filled type vibration damping device, a first mounting member is attached to a power unit while a second mounting member is attached to a vehicle body, thereby providing vibration damping support of the power unit on the vehicle body.
Here, a bracket has been employed as a separate element that is adapted to be secured onto the outside peripheral face of the second mounting member for attaching the tubular second mounting member to the component to be provided with vibration damped linkage such as the vehicle body or the like. While a metal bracket has been used as the separate bracket to date, in recent years, employing a resin bracket has been contemplated because of the growing needs of vehicles reduced in weight.
For example, Japanese Unexamined Patent Publication No. JP-A-6-234134 discloses a technique wherein a main rubber of the vibration damping device has been formed by vulcanization molding in advance, the main rubber is set in a resin mold for injection molding of a resin so as to produce a resin bracket of the device, and the resin bracket and the main rubber are bonded to each other utilizing pressure and heat during the injection molding. However, for bonding the resin bracket directly to the main rubber in this way, it is necessary to perform an adhesive treatment (apply an adhesive) on the surface of the main rubber. This will pose a problem of increasing production cost for the adhesive as well as the number of steps for applying the adhesive.
In order to address this problem, Japanese Unexamined Patent Publication No. JP-A-2001-50331 proposed a construction in which a second mounting member is furnished with annular projections on its outside peripheral face at two or more sections spaced apart from one another in the axial direction. The second mounting member is subjected to an insert molding with a resin bracket so that the annular projections are inserted into and pinched by the resin bracket, thereby obtaining bond strength without increase in production cost for the adhesive as well as the number of steps for applying the adhesive. However, with the construction wherein the two or more annular projections are inserted into the resin bracket in this way, residual stress tends to be generated in the resin portion clasped between the annular projections. Thus, strength or durability as a resin bracket is likely to be deteriorated.
As reasons for this, it is posited that in the resin portion clasped between the upper and lower annular projections in the axial direction, which includes most of the resin portion of the resin bracket in the axial direction, the upper and lower annular projections will inhibit the resin from shrinkage after the injection molding. Appreciable residual stress will be generated thereby, posing a risk that strength or durability as a resin bracket may be deteriorated and hence cracking may occur.
Another problem is that since the lower annular projection of the second mounting member has U-shaped contours bent by 180 degrees, which is more complicated structure than that of the upper annular projection, increase in production cost by a corresponding amount will be inevitable. Moreover, there is another inherent problem that because the entireties of the upper and lower annular projections of the second mounting member are covered by the resin portion so as to be embedded therein, a large volume of resin will be required in order to cover the axially outside of the annular projections as well, inevitably causing increased weight.